For a number of years, the National Aeronautics and Space Administration has had a monumental task in aligning the joints of very large cylinders so that they can be welded together for the purpose of assembling fuel tanks for space vehicles. One such application occurs in assembling the external tank for the space shuttle, an application which requires welding together two very large cylinders about 27 feet in diameter, which are butted together end-to-end. In this case the problem is accentuated by the fact that the joint must be strengthened by inserting a strengthening section or tee ring between the mating ends of the two large cylinders. The tee-ring, which adds strength to the joint because it has a cross section somewhat like an I-beam, has two lower flanges which have the same diameter and thus mate with the ends of the two large cylinders.
In the past a large mandrel-type assembly tool has been used to hold the cylinder assemblies in position for the welding operation. However, mandrel tooling is expensive and cumbersome to use. Mandrels do not offer the very precise mating ability that is needed in this application. Therefore, the National Aeronautics and Space Administration has had a continuing need for a better way to precisely align and hold these large diameter cylinders in position for welding. Obviously, in the manufacture of space vehicles, greater accuracy, precision, and strength are required than in other, more routine manufacturing applications involving the assembly of much smaller cylinders.
The prior art discloses a number of devices for temporarily aligning the ends of cylindrical pipes in order to weld them together. One such device is disclosed in U.S. Pat. No. 3,952,936 to DEARMAN. The DEARMAN patent discloses a pair of metal bands which form an annulus adapted to encircle one of the pipe sections. The two metal bands are joined together by metal web members spaced circumferentially around the annulus. The web members extend outward at a right angle to the metal bands above the surface of the second pipe sectin. The end of each web member is equipped with a force supplying screw to conform the configuration of the first pipe section to that of the second. Each web member has a flange through which extends a threaded adjusting screw that is adapted to engage the outer surface of the second pipe. This DEARMAN device, while it appears to be an effective device for conforming one pipe section to the end of a second pipe section, would not be an effective way to join two very large cylinders which have a reinforcing section between the ends of the cylinders.
A second patent to DEARMAN, U.S. Pat. No. 4,356,615 shows a device for aligning two large pipes for welding. This device has two substantially coaxial annular clamps for encircling the two mating pipe sections. This device is operative to put pressure on the outside of one pipe to bring the circumference into a certain configuration. Pressure is then executed against the outside circumference of the second pipe to bring it in to a similar configuration. Finally the two sections are pulled toward each other to bring them into final position for welding. This invention contains means to affect rocking and axial movements and shifting means to affect transverse movements of the two large clamps. Thus the structure of this device appears to be complicated and expensive and would be too elaborate to upsize for mating cylinders having a diameter of about 27 feet.
Another prior art device is disclosed in U.S. Pat. No. 3,467,295 to WATSON. WATSON discloses another device for securing pipe sections in proper alignment to facilitate welding them. The WATSON device has an annular metal band having a compression clamp which is used to force the ends of the annular member toward one another. The annular member fits around one pipe section near its end. A series of clamping arms are spaced circumferentially around the annular metal band. One end of the clamping arms is secured to the metal band and the other end of the clamping arm extends parallel to the pipe assembly access over the second section of pipe. The ends of the clamping arm contain threaded bolts with pointed ends which may be selectively engaged upon the second pipe section to allow proper pipe alignment. This device is really only suitable for the purpose of aligning small circumference pipes. Moreover, it will only conform one pipe section to the circumference of the other pipe section, but will not adjust the two pipe sections relative to each other. This device could not be upsized to align very large diameter cylinders.
A second patent to WATSON, U.S. Pat. No. 3,666,159, which is a continuation-in-part of the earlier WATSON patent discloses similar structure except that a link chain is used instead of an annular metal band. This device, like the earlier WATSON device, could not be upsized to align very large diameter cylinders.
The prior art includes several other pipe clamping devices which have chains extending around the circumference of a pipe to position jacks or shoes which configure the end of one pipe in order to make it mate with the end of another pipe for welding. These devices are all designed for use in welding the ends of small pipes together and could not be upsized so as to be suitable for assembling very large cylinders.
U.S. Pat. No. 4,195,828 to PETERSON discloses a boiler tube welding clamp which fits around the end of one tube and has a jack screw which puts pressure on the end of a second tube and brings it into alignment with the end of the first tube. Again, this device is designed for use with comparatively small tubes and would not be at all suitable for use in aligning the ends of very large cylinder of the order to twenty-seven feet in diameter.
U.S. Pat. No. 3,619,891 to Harrison discloses an aligning pipe clamp which will allow abutting pipe ends to be welded together. The clamp consists of a plurality of spaced aligning block members, each having an adjustable screw and contact foot. Each of the blocks receives a roller chain which is held in place by means of a ratchet so that the blocks may slide along the external surface of the pipes.
U.S. Pat. No. 3,722,038 to ARNTZ et al. discloses a device for holding pipe sections together for welding comprising pipe clamping shoes held in place by chains extending around the outside of the pipe sections. Each shoe contains threaded pipe-positioning members which can be radially adjusted to engge one of the pipe sections.
U.S. Pat. No. 1,916,556 to BUTT discloses a clamp which may be used with an elongated clamping bar, having an angular cross section, to bind together two lengths of metal pipe before welding. The clamp includes a jaw, engageable by means of a screw, and a ligature, adapated to be wrapaped araound teh pipe and clamping bar.
A primary object of this invention is to provide an alignment tool which is capable of aligning very large cylinders which are butted together end-to-end so that the joint may be welded.
Another object of this invention is to provide an alignment tool which may be installed on the inside surfaces of very large cylinders to align them so that they may be welded together end-to-end.
Still another object of this invention is to provide an alignment tool which is capable of aligning two very large cylinders which are butted together end-to-end, when a cylindrical stengthening section (tee ring) having an up-right, generally I-beam shaped cross section is positioned between the two ends of the very large cylinders.
A fourth object of this invention is to provide an alignment tool for very large cylinders which is capable of aligning two large cylinders butted together end-to-end for welding and which is capable of achieving more precise mating abililty than is possible through the use of mandrel tooling previously used for this purpose.
A fifth object of this invention is the achievement of substantial cost savings over the use of expensive mandrel tooling previously used to align two very large cylinders for the purpose of welding their end sections together.